Dubois, who added an assist, has three goals in three games since his return after missing 47 games because of surgery he had to address injuries to his abdominal and adductor muscles.
Jakob Chychrun also scored for the Capitals (31-23-7) who have won three straight and six of seven. Aliaksei Protas and Rasmus Sandin each had two assists, and Logan Thompson made 24 saves.
Braeden Bowman and Tomas Hertl scored third-period goals for the Golden Knights (28-17-14), who had won three straight. Akira Schmid made 26 saves.
Dubois gave the Capitals a 1-0 lead 49 seconds into the second period. Protas passed the puck back to Dubois on the rush and his snap shot from the top of the right circle deflected in off Schmid’s right shoulder.
Dubois made it 2-0 at 3:23 when Protas got to a loose puck behind the net and passed out to Dubois, who scored on a one-timer from the low slot.
Chychrun increased the lead to 3-0 at 14:52 when he beat Schmid on a high one-timer from just below the right face-off dot off a pass from Sandin.
Bowman pulled the Golden Knights within 3-1 at 2:27 of the third period. Kaeden Korczak’s pass on the rush appeared to deflect off Washington’s Declan Chisholm and Bowman got to the puck behind the defense and scored over Thompson’s left pad.
Hertl made it 3-2 at 9:15, scoring from the slot when his redirect of a Pavel Dorofeyev pass deflected off defenseman Matt Roy’s skate and past Thompson during a power play. The goal was Hertl’s 600th NHL point.
Thompson stopped Brayden McNabb on a breakaway with 4:09 remaining.
